The original idea by Johan Perjus, from https://medium.com/design-bootcamp/things-i-wish-adobe-would-address-with-adobe-illustrator-4796a89e1bae

Units of measure settings are a mess right now, units can be set for General, Stroke and Type on a “global” level under Illustrator > Preferences, but “General” are overridden by Unit settings on document (local) level, however it does not apply to, nor can it be changed for Stroke and Type on document level. Thus adds a lot of unnecessary back and forth visits to Preferences > Units if you are working with delivery for different mediums (who isn’t?) print, web, motion graphics and so on, add multiple markets to that (imperial vs metric) and it becomes a bit of a mess.

See one of two attached images for an example of the confusion around units of measure that is currently plaguing Adobe Illustrator (26.5)

I therefore suggest that a checkbox option to “Honor” or “Translate” Units of measure are added to Preferences > Units, or are removed from Global Preferences altogether, more on that later.

See the second image, an animation of a screenshot of the Adobe Illustrator Preferences > Units panel proposing adding a checkbox at the top to either “Honor” or “Translate” any units of measure input to the software interface.

The “Honor Unit Input” setting will change the unit of measure setting to any unit of measure added in conjunction with a value in any given numeric input field (cm, mm, ft, feet, in, inches, ', ", px, pixels). Similar to how numeric input for Height and Width values are currently implemented in Photoshop**.

Example; if you enter “4 px” in the stroke width input field, the stroke width will transform to, and display as 4 pixels wide and also change the document unit settings for Stroke to Pixels, thus change current and/or override previous settings or preferences until changed. Obviously only entering “4” will only change the value and not the unit of measure.

“Translate Unit Input” will translate the unit of measure entered to the unit of measure selected in the document settings and/or preferences.

Example; if you enter “1 in” (or 1") in the stroke width input field and the stroke width preferences are set to Millimeters (global or local), the stroke width will transform and be converted to the equivalent width in millimeter value and display as 2,54 mm.

Now I imagine the use cases where one would want to input in one unit of measure and yet have it display as another would be rare, hence why one could consider to simply remove Units from Preferences altogether.

Instead simply make all numeric input fields behave as described under “Honor Unit Input”, however the “Translate” option could be useful in some cases, for example if one would need to output work in Metric but is more familiar or comfortable working in Imperial, or vice versa. But for the above reason I suggest the default Unit Preference setting would be “Honor Unit Input”.